The seal structure by an annular seal member is used in various fields such as valves, hydraulic devices, and the engine of an internal combustion engine. Patent Document 1 discloses, in relation to the engine of an internal combustion engine, a seal structure by a upper and lower two seal rings which are fit in ring grooves of a piston which is sloped upwards so as to approach a cylinder head as approaching an inner peripheral wall of the cylinder.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2005-282370